Pipeline pigs

ABSTRACT

This invention provides a pipeline pig for transporting electrical circuitry through a pipeline. The pipeline pig includes a pressure-sensitive switch on the housing which is designed to electrically activate the electrical circuitry when the internal pipeline pressure exceeds a predetermined level. When the pressure does not exceed that level, the electrical circuitry remains inactive.

Umted States Patent [191 [111 3,732,434 French 1 May 8, 1973 [54]PIPELINE PIGS [56] References Cited Inventor: Hartley A. French,willowdale, On-

tario, Canada 2,951,362 9/l960 Dean et al ..73/40.5 R [73] AssigneezTrans-Canada Pipe Lines Limited,

Toronto Oman), Canada I Primary Examiner-Herman J. Hohauser [22] Filed:Mar. 2, 1972 Attorney-R. Gordon Waldie [21] Appl. N0.: 231,217 57ABSTRACT This invention provides a pipeline pig for transporting [52]U.S. Cl. ..307/118, l5/lO4.6 R, 73/40.5 R electrical circuitry through ai l The pipeline pig [51] Int. Cl. "H0"! 35/18 i lud s apressure-sensitive switch on the housing of Search is designed t0electrically activate the electrical 15/1045 346/33 circuitry when theinternal pipeline pressure exceeds a 118 predetermined level. When thepressure does not exceed that level, the electrical circuitry remainsinactive.

6 Claims, 2 Drawing Figures PATENIEB 3,732,434

ELECTRONIC EQUIPMENT. l I 25 BATTERY PIPELINE PIGS This inventionrelates to improvements in pipeline pigs commonly used for a variety ofpurposes in fluidcarrying pipelines.

The pipeline industry conventionally utilizes pipeline pigs toaccomplish certain specialized operations inside pipelines. Commonly,pipeline pigs include an elongated body which is retained centrally ofthe pipeline by two or more flexible, radially outwardly extendingscraper cups spaced apart longitudinally and fitting snugly but slidably(due to their resilience) within the pipeline.

Pipeline pigs are forced through the pipeline by pressure from the fluidbehind the pig exerted on the body of the pig and on the scraper cupsattached thereto.

The body of a pipeline pig can support brushes, scrapers, or otherdevices for cleaning the interior wall of the pipeline. Other pipelinepigs do not carry cleaning elements, but are used simply as separationpigs for separating two different fluids being consecutively passedthrough the pipeline. Still other pipeline pigs are used to remove fluidtrapped at low spots in the pipeline. There are also in use certainkinds of pipeline pigs which carry checking and measuringinstrumentation through the pipeline to measure fluid characteristics,to check the pipeline itself, or to accomplish any of a large number ofmeasurements or safety checks necessary to the proper maintenance andoperation of a pipeline.

It is to this latter group of pipeline pigs, those carryinginstrumentation through the pipeline, that this inverition particularlyrelates.

The ever-increasing use of instrument-carrying pigs in pipelinesnecessarily carries with it certain considerations regarding safety.When such instrumentcarrying pigs utilize electrical circuitry, and whenthe pipeline is carrying a fluid that forms an explosive mixture withair, it becomes highly desirable to ensure that the construction of thepipeline pig permits no contact between an electrical spark in thecircuitry and the region where the explosive mixture may be formed.

Because of the above-mentioned danger of explosion with pipeline pigscarrying spark-producing electrical circuitry with an energy levelsufficient to cause an explosion in a hazardous atmosphere, it is anobject of this invention to provide a pipeline pig in which the risk ofexplosion through spark-producing circuitry is minimized.

It is a further object of this invention to provide a pipeline pig forcarrying spark-producing electrical circuitry, in which the circuitry isnot activated until a predetermined operating pressure has been achievedinside the pipeline behind the pipeline pig.

Accordingly, this invention provides a pipeline pig for transportingelectrical circuitry through a pipeline, the pipeline pig comprising: ahousing supporting said electrical circuitry, means for supporting thehousing for translational movement within the pipeline, and apressure-sensitive switch on the housing adapted to electricallyactivate said electrical circuitry when the internal pipeline pressureexceeds a predetermined level, and adapted to render the electricalcircuitry inactive when the internal pipeline pressure does not exceedsaid predetermined level.

In a preferred embodiment, the housing is pressure tight, and containsas much as possible of the electrical circuitry and battery means forenergizing the circuitry. The housing is filled with an inert gas suchas nitrogen at a low pressure, and the pressure-sensitive switchoperates on the basis of the differential between the pipeline pressureand the pressure inside the housing. This ensures that, if the housingshould develop a leak, the internal housing pressure would rise to thesame level as that in the pipeline, thereby eliminating any differentialbetween the pipeline and the housing, and thus opening thepressure-sensitive switch to cut the connection between the electricalcircuitry and the battery means.

One embodiment of this invention is shown in the accompanying drawings,wherein like numerals denote like parts throughout the several views,and in which:

FIG. 1 is a perspective view of a pipeline pig embodying this invention;and

FIG. 2 is a schematic diagram showing the principal features of theelectrical circuit in the pipeline pig of FIG. 1.

In FIG. 1, a pipeline 10 shown in broken lines is seen to contain apipeline pig 12. The pipeline pig 12 generally includes a pig body 14, aforward scraper cup 16, and a rear scraper cup 18. The pig body 14 ismade up of a central, pressure-tight housing 20 which is shown in theshape of a rectangular parallelepiped but which may have any appropriateconfiguration, a forward cylindrical extension 22 and a rearwardcylindrical extension 24. The configuration of the pig body 14 forms nopart of this invention.

The desired electronic equipment 25 and one or more batteries 26 arehoused within the pressure-tight housing 20, as shown in broken lines inFIG. 1. The specific construction of the electronic equipment and thebatteries forms no part of this invention, and so no detaileddescription is here included. The electronic equipment 25 could betesting, measuring and/or recording equipment of the kind conventionallytransported in instrument-carrying pipeline pigs.

The scraper cups l6 and 18 are of conventional shape, resembling hollowspherical segments attached at their axes of symmetry to the ends of therespective cylindrical extensions 22 and 24. Both of the scraper cupsopen in the same direction, i.e. rearwardly with respect to thedirection of travel of the pipeline pig 12, the latter being to theleft. At the distal end of each cylindrical extension 22 and 24 arelocated two cup flanges 27 between which the respective scraper cup issandwiched. Only one cup flange 27 is visible at the end of eachcylindrical extension, because the respective scraper cup hides theother one.

In the rear face 28 of the rearward cylindrical extension 24 is locateda pressure-sensitive switch 30 of which the pressure sensing element 31is exposed to the fluid pressure within the pipeline immediately to therear of the pig, while the electrical switching element 32 (operated bythe pressure sensing element 31) is located inside the pressure-tightcylindrical extension 24 so that it is in no way exposed to the contentsof the pipeline. The pressure-sensitive switch 30 is preferably onewhich operates on the differential between the pressure in the pipelineand the pressure inside the housing 20. Preferably, the housing containsnitrogen at a very low pressure, for example 1 psia. When apredetermined pipeline pressure is reached, say 25 p.s.i. in excess ofthe internal housing pressure, the electrical switching element 32 isclosed.

As seen in FIG. 2, the electrical switching element 32 is adapted toopen and close the electrical connection between the battery 26 and theelectronic equipment 25. Unless the pressure differential between thepipeline interior and the housing interior exceeds a given predeterminedamount, the electrical switching element 32 remains open.

With this preferred construction, the electronic equipment in thepipeline pig is not electrically alive until the pipeline pressurereaches a predetermined amount, and it is possible to ensure that fullline pressure is achieved only after all air has been purged from thepipeline and the pig launcher.

Another advantage of this preferred construction of the pipeline pigdescribed above is that, should the housing 20 begin to leak, the fluidin the pipeline would enter the housing and very soon would equalize thepressures inside and outside the housing. This would cause thepressure-sensitive switch 30 to open, and disconnect the battery fromthe electrical equipment, thus eliminating the risk of sparking.

To permit the pressure-tight housing 20 to be purged of air and filledwith an inert gas at low pressure, such as nitrogen, two connectors 38and 40 are provided in the rear face 28 of the cylindrical extension 24.

A hermetically sealed multiple electric socket 42 is provided for thepurpose of conveying the sensing circuits through the housing wall fromthe interior of the housing.

In the preferred method of using the pipeline pig described above, thepig is first inserted in the launcher apparatus, the launcher is thensealed, nitrogen (as a typical inert gas) under pressure is theninjected into the launcher in the space between the scraper cups l6 and18 and behind the rear scraper cups 18 so that any air can be purged,and natural gas is then allowed to flow into the pipeline ahead of theforward scraper cup 16. The gas is allowed to flow out at the downstreamend until all air in the pipeline has been purged. The pig trapapparatus is located at the other end (the downstream end) of thepipeline section under test, and the pipeline pig travels to and becomescaught in the pig trap apparatus. By following the foregoing practice,the risk of an explosion, already greatly reduced by virtue of theconstruction of the pipeline pig, is further minimized because at notime does a mixture of air and natural gas exist in the area where thepig is located.

It is to be understood that the switch 30 could be one which operatesindependently of the internal housing pressure. For example, anevacuated bellows-type pressure-sensing switch could be employed, whichsenses the effective differential between its own vacuum and theinternal pipeline pressure.

An additional safeguard against the risk of explosion from a sparkingcircuit is the encapsulation in plastic of as much as possible of theelectrical circuitry, particularly that portion of the latter which mayof necessity be carried on the outside of the housing or in some otherwa be ex osed tothe fluid in the pi eline.

A fur er sa ety precaution would be t e restriction that all circuitsexternal to the pressure tight container shall be limited to signalcircuits operating at energy levels below that needed to cause anexplosion in the event that a spark were caused by broken wires or someother defect.

What I claim is:

l. A pipeline pig for transporting electrical circuitry through apipeline, the pipeline pig comprising:

housing means supporting said electrical circuitry,

means for supporting the housing means for translational movement withinthe pipeline,

sealed chamber means maintaining an internal pressure lower than theworking pressure of the pressurized pipeline,

and a pressure-sensitive switch on the housing adapted to electricallyactivate said electrical circuitry when the pressure in the pipelinelongitudinally adjacent the pig exceeds the pressure within said chambermeans by at least a predetermined amount, and adapted to render theelectrical circuitry inactive when the pipeline pressure does not exceedthe pressure within said chamber means by at least said predeterminedamount.

2. A pipeline pig for transporting battery means and electricalcircuitry through a pressurized pipeline, the pipeline pig comprising:

a pressure-tight housing containing said electrical circuitry, thepressure within said housing being lower than the working pressure ofthe pressurized pipeline,

scraper-cup means for supporting the pressure-tight housing within thepipeline,

and a pressure-sensitive switch on the housing adapted to electricallyconnect said battery means with said electrical circuitry when thepressure in the pipeline longitudinally adjacent the pig exceeds thepressure within said housingby at least a predetermined amount, andadapted to open the electrical connection between the battery means andthe electrical circuitry when the pressure in the pipelinelongitudinally adjacent the pig does not exceed the pressure within saidhousing by at least said predetermined amount.

3. The invention claimed in claim 2, in which the housing has connectormeans by which it can be filled with an inert gas. I

4. The invention claimed in claim 2, in which the housing containslow-pressure nitrogen.

5. The invention claimed in claim 2, in which some at least of theelectrical circuitry is encapsulated in plastic.

6. The invention claimed in claim 2, in which the pressure-sensitiveswitch senses the pipeline pressure to the rear of the pipeline pig.

1. A pipeline pig for transporting electrical circuitry through apipeline, the pipeline pig comprising: housing means supporting saidelectrical circuitry, means for supporting the housing means fortranslational movement within the pipeline, sealed chamber meansmaintaining an internal pressure lower than the working pressure of thepressurized pipeline, and a pressure-sensitive switch on the housingadapted to electrically activate said electrical circuitry when thepressure in the pipeline longitudinally adjacent the pig exceeds thepressure within said chamber means by at least a predetermined amount,and adapted to render the electrical circuitry inactive when thepipeline pressure does not exceed the pressure within said chamber meansby at least said predetermined amount.
 2. A pipeline pig fortransporting battery means and electrical circuitry through apressurized pipeline, the pipeline pig comprising: a pressure-tighthousing containing said electrical circuitry, the pressure within saidhousing being lower than the working pressure of the pressurizedpipeline, scraper-cup means for supporting the pressure-tight housingwithin the pipeline, and a pressure-sensitive switch on the housingadapted to electrically connect said battery means with said electricalcircuitry when the pressure in the pipeline longitudinally adjacent thepig exceeds the pressure within said housing by at least a predeterminedamount, and adapted to open the electrical connection between thebattery means and the electrical circuitry when the pressure in thepipeline longitudinally adjacent the pig does not exceed the pressurewithin said housing by at least said predetermined amount.
 3. Theinvention claimed in claim 2, in which the housing has connector meansby which it can be filled with an inert gas.
 4. The invention claimed inclaim 2, in which the housing contains low-pressure nitrogen.
 5. Theinvention claimed in claim 2, in which some at least of the electricalcircuitry is encapsulated in plastic.
 6. The invention claimed in claim2, in which the pressure-sensitive switch senses the pipeline pressureto the rear of the pipeline pig.